Members of either House of the Oireachtas (Dáil or Seanad) may be appointed to be a Minister of State at a Department of State; however to date no senator has been appointed. Like a senior minister, Ministers of State continue in office after the dissolution of the Dáil until a successor is appointed. If the Taoiseach resigns from office, a Minister of State is also deemed to have resigned from office. As the duties of the Minister of State are delegated from a Government Minister, they must be re-appointed if that Government Minister resigns.

The post of Minister of State was created by the Ministers and Secretaries (Amendment) (No. 2) Act 1977 and commenced in 1978, and under the Act a Minister of State may be delegated a power or duty of the Minister of the Government they support. The position was created to replace the post of parliamentary secretary, the junior rank of ministers which had existed from 1922 until 1978. In the Irish Free State, the Ministers and Secretaries Act 1924 created the post of Parliamentary secretary, originally limited to seven holders.

In the act of 1977 the number of Ministers of State was limited to 10, but in 1980 this was raised to 15, and in 1995 it was raised to 17, and in 2007 it was raised to 20. Brian Cowen asked all 20 Ministers of State to resign on 21 April 2009. He re-appointed a reduced number of 15 ministers the following day, when the Dáil resumed after the Easter recess.[1][2] As of June 2017, there are 19 Ministers of State.

Máire Geoghegan-Quinn was the first woman to be appointed as a Minister of State when she as appointed by Jack Lynch as Minister of State at the Department of Industry, Commerce and Energy in 1978. She had previously been the first woman to be a Parliamentary Secretary in 1977.

Some Ministers of State attend cabinet meetings but do not have a vote. The Government Chief Whip automatically attends and starting in the 1990s some governments appointed an additional Minister of State with permission to attend cabinet but not vote thereat. Two were appointed in 2016 upon Enda Kenny's re-election.

The Ministers, other than the Chief Whip are usually described as a "Super Junior" minister.[3] or sometimes more formally as "Minister of State attending cabinet". The Super Juniors of the 31st Government are:

Some Ministers of State are de facto department heads. In the 31st Government, Leo Varadkar is the Minister for Defence but the day to day running of the department is done by Paul Kehoe, the Minister of State for Defence.